1. Field of the Invention
The present invention relates generally to substrate handling, and more particularly, to towers for positioning substrates and to methods of efficiently manufacturing the towers, components of such towers, and end effectors using such towers and components.
2. Description of the Related Art
Transport chambers are generally used in conjunction with a variety of substrate processing chambers, which may include semiconductor processing systems, material deposition systems, and flat panel display processing systems. Growing demands for cleanliness and high processing precision increase the need for reduced amounts of human interaction between the processing steps. This need has been partially met by transport chambers, which operate as intermediate handling apparatus between such processing steps.
In the use of transport chambers, when a substrate is required for processing, a robot arm within the transport chamber may be used to retrieve a selected substrate from storage and place it into one of the multiple processing chambers. Transport of substrates among multiple storage facilities and processing chambers is typically referred to as cluster tool architecture.
FIGS. 1A and 1B schematically illustrate a typical cluster tool architecture. Substrates 101 may be stored in a clean room 102. The substrates 101 may be the base on which layers are deposited in semiconductor processing, or by the material deposition systems, or may be a support used in the flat panel display processing systems, for example. Such substrates are very fragile, giving rise to a need to carefully handle the substrates. The substrates 101 are commonly referred to as wafers.
A load lock 104 is generally coupled to the clean room 102. In addition to being a retrieving and serving mechanism, the load lock 104 also serves as a pressure varying interface between the clean room 102 and a transport chamber 106 that interfaces with various processing chambers 108a-108c. FIG. 1B shows in more detail a cassette 110 in the clean room 102 for storing the substrates 101. The load lock 104 has a prior art end effector 112 within it. A drive assembly 114 serves to move an arm assembly 116 connected to the end effector 112. As described below, the prior art end effector 112 is made by alternately stacking prior art spatulas 118 and spacers 120. The load lock 104 also interfaces with the various processing chambers 108a-108c by way of a main robot arm 122 of the transport chamber 106.
In use, the end effector 112 of the load lock 104 is moved through a port 124 of the clean room 102 and receives a supply of the wafers 101. In detail, each spatula 118 receives one of the wafers 101 from the cassette 110 and supports the wafer 101 for transport. The end effector 112 is then moved out of the clean room 102 and back into the load lock 104, where the wafers 101 are stored prior to being used for processing. Such processing is initiated by the main robot arm 122 reaching into the load lock 104 and removing one of the wafers 101 from the supported position on the spatula 118.
It may be appreciated that two wafer transfer operations are required to move the wafers 101 from the clean room 102 into a processing chamber 108, and that each such transfer operation is to be accomplished without human intervention. For the first transfer, the spatulas 118 of the end effector 112 must be aligned with the wafers 101 contained in the cassette 110. If not aligned, horizontal movement of the end effector 112 toward the cassette 110 may cause one or more of the spatulas 118 to move horizontally and hit one or more of the wafers 101. Such hitting may break the wafers 101, or otherwise damage the wafers 101, as by scratching an upper device surface 126, of the wafers 101. While this type of damage to a wafer 101 is a significant cost factor in such processing, a greater cost factor results when the end effector 112 is not aligned with the main robot arm 122 in a second wafer transfer operation. For example, when the processing of the wafer 101 is substantially complete, the value of the wafer 101 includes the increased cost of the processing that has taken place since the wafer 101 left the clean room 102. However, the first wafer transfer operation has a greater potential of damaging multiple wafers, resulting in a higher cost of production.
Attempts have been made to provide end effectors 112 with spatulas 118 accurately aligned with both the cassette 110 (and the wafers 101 therein) and the main robot arm 122. One such attempt is to make a stack of alternating spatulas 118 and spacers 120 as shown in FIG. 1C. There, bolts 132 are illustrated for squeezing the spatulas 118 and the spacers 120 together to form the end effector 112. Referring to FIG. 1C, a desired relative positioning of the spatulas 118 is depicted by reference lines 128. This desired relative positioning will properly align each spatula 118 with the wafers 101 that are in the cassette and with the robot arm 122 for transfer among the cassette 110, the load lock 104, and the transport chamber 106. To achieve the desired relative spacing of the spatulas 118 of the end effector 112, attempts are made to hold the thickness T of every one of the spacers 120 and every one of the spatulas 118 within a very close tolerance. For example, the same desired relative positioning is indicated in FIG. 1D by the reference lines 128. However, the actual relative positioning (shown by reference lines 130 and 130U) differs significantly from the desired relative positioning even though the spatulas 118 and the spacers 120 are within the desired tolerance (are in-tolerance). In this example, the significant difference is due to the thickness TT of spacers 120TT being at the thick end of the tolerance. Such thicknesses TT are shown in FIG. 1D accumulating, and resulting in and in-tolerance spacer 120 and the in-tolerance upper spatulas 118U being positioned above the reference lines 128 and 128U, indicating misalignment of the spatulas 118U. Such misalignment of the spatulas 118U with the reference lines 128 and 128U resulting from the accumulation of tolerances is referred to as tolerance stacking. Although not shown in FIG. 1D, such misalignment of the spatulas 118U with the reference lines 128 may also result from the accumulation of tolerances that are at the thin end of the desired tolerance. Tolerance stacking is a significant cause of the wafer damage problem described above.
These misalignment problems not only cause the noted wafer damage problems, but may also result in damage to the prior art end effectors 118. Such end effector damage may require retooling of the prior art end effector 118, such as by shutting down the operation of the load lock 104, removing the prior art end effector 112 and replacing any broken spatulas 118, for example.
It may be appreciated that the use of the stacked spatulas 118 and the spacers 120 for the prior art end effectors 112 is dependent on the success of expensive efforts to make each of the spatulas 118 and each of the spacers 120 within very tight tolerances, e.g. plus or minus 0.0005 inches. Also, selection of spatulas 118 and spacers 120 for use in a particular end effector 112, and other costly steps necessary to attempt to reduce tolerance stacking in stacked arrangements of spatulas 118 and spacers 120, give rise to an unfilled need to avoid using the stacked arrangements. Further, when these expensive manufacturing efforts fail, the noted significant cost factors (e.g., damage to an unprocessed wafer 101, or misalignment of the end effector 112, causing damage to a wafer 101 that has been substantially completely manufactured), are but a part of the resulting costs because process shut-down and reworking of the end effectors 112 may also be required to correct the end effector misalignment. Of course, any shut down situation tends to reduce the yield or productivity of the processing and should be avoided.
In addition to these direct costs resulting from such misalignment problems, the risk of contamination is a factor in the prior art end effectors 112 due to the multiple separate parts that are used to make such end effectors 112.